The present invention relates to ophthalmic lenses.
Multifocal progressive lenses are now well known. They are used for correcting long-sightedness and enable the spectacle wearer to observe object over a wide range of distances without removing the spectacles. Such lenses typically include a far vision region situated in the upper portion of the lens, a near vision region situated at the bottom of the lens, an intermediate region linking the near and far vision regions, as well as a main meridian of progression which passes through these three regions. French patent application FR-A-2,699,294 discusses, in its preamble, the various elements of such a multifocal progressive ophthalmic lens along with the work carried out by the applicant to improve comfort of wearers of such lenses. This document should be consulted for more information on these various points.
Wearers generally have difficulties in adapting to progressive lenses. Because of this, a certain number of long-sighted people for whom such progressive lenses could be prescribed, do not adopt them. This notably concerns young long-sighted people with no ametropia, or long-sighted people with only slight ametropia. Such wearers will be satisfied with single-focus lenses or bifocals. These solutions are not satisfactory as they do not provide correction for intermediate vision, and are not aesthetic.
A lens has been proposed (see article in the "Opticien Lunetier" dated April 1988), sold commercially by the applicant under the Essilor Delta trademark; this lens is also as simple to use and easy to wear as a progressive lens, and it is attractive to long-sighted people not fitted with progressive lenses. This lens is also described in French patent application 2,588,973. It has a central portion which is equivalent to the single-focus lens that would normally have been employed for correcting long sightedness, in order to ensure satisfactory near vision. It additionally has a slight decrease in power in the upper portion, ensuring that the wearer also has sharp vision beyond the usual near vision field. Finally, the lens has a point at a power value equal to the nominal power for near vision, a higher power region at the lower portion of the lens, and a lower powered region in the top portion of the lens.
This lens suffers from disadvantages; it causes problems with dynamic vision resulting from a too high power in close vision and a too low power in intermediate vision, for the mounting instructions envisaged. In peripheral vision, the lens has significant astigmatism; the region of progression between the central portion and the upper portion is of reduced width.